A Long-Term Record of Upper Stratospheric and Mesospheric Temperature Profiles

Long-term data records of temperature profiles spanning the upper stratosphere and mesosphere (US/M hereafter) are sparse and intermittent. This region is, however, far more sensitive to climate change than is the lower atmosphere: US/M temperature trends of ~2-3 K/decade have been reported, compared to ~0.2 K/decade at lower altitudes. We will produce a long-term observational dataset of daily, near-global US/M temperature profiles from roughly 25-80 km altitude covering 1991 to the present. This unique and valuable new record spanning over 20 years will facilitate studies that advance our understanding of US/M processes, how those processes are affected by climate change, and coupling of the US/M to the lower atmosphere.

The record will include observations from the Microwave Limb Sounder (MLS) on the Aura satellite (launched in 2004) and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere, Ionosphere, Mesosphere, Energetics, Dynamics (TIMED) platform (launched in 2002). Data for 1991 to 1998 will be taken from the earlier MLS instrument on the Upper Atmosphere Research Satellite (UARS) platform (launched in 1991). The record will be augmented with more-coarsely-sampled (approximately monthly global coverage) solar occultation observations from the Halogen Occultation Experiment (HALOE) on UARS, the Fourier Transform Spectrometer (FTS) instrument on the Canadian Space Agency Atmospheric Chemistry Experiment (ACE) (launched in 2004) mission, and the Solar Occultation for Ice (SOFIE) instrument on the Aeronomy of Ice in the Mesosphere (AIM) (launched in 2007) mission. The UARS HALOE record will be used, in conjunction with long-term ground-based records from lidar, to bridge the gap between the UARS and TIMED/Aura periods. Biases between all the datasets will be quantified and 'bias-corrected' datasets will be generated and validated.

To accomplish these objectives, we will:

Produce a 'definitive' record of US/M temperature from UARS MLS: The operational use in retrievals of a model with polarized radiative transfer calculations, required for accurate temperature retrievals in the mesosphere, was not computationally feasible during the UARS era. Advances in computing power make possible the application of the algorithms and software developed and proven for the later Aura MLS instrument to UARS data.

Produce an 'independent' record of US/M temperature from Aura MLS: Current Aura MLS retrievals are focused on providing the most accurate record of atmospheric composition, at the expense of some simplifications and approximations in processing the temperature observations. They use daily meteorological analysis fields as a priori constraints, which could result in biases in long-term trends. The Aura MLS record will be reprocessed to remove these issues.